Resistance-capacitance coupled amplifier



Dec. 26, 19331 w. A. FITCH RESISTANCE CAPACITANCE COUPLED AMPLIFIER Filed April H is Attdr-ney.

Patented Dec. 26,

PATENT OFFICE RESISTANCE-CAPACITANCE COUPLED AMPLIFIER William A. Fitch, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 28, 1932.

Serial No. 608,021

6 Claims. (Cl. 179-171) My invention relates to amplifiers and more particularlyto impedance or resistance-capacitance coupled amplifiers for operation over a wide range of audio and radio frequencies.

In television transmitters and receivers it is necessary to provide amplification for the frequency impulses which produce the television image. Such frequency impulses may range from an audio frequency of 20 cycles to a radio frequency of 200,000 cycles or more. For the amplification of such frequencies which include both audio and radio frequencies, the ordinary resistance-capacitance coupled amplifier has beenused, but the coupling capacitor introduces a large phase shift at the low audio frequencies which has the efiect of shifting the various lines of the television image so that the picture becomes distorted.

My invention has for one of its objects to provide an amplifier with a resistor-capacitor means for neutralizing the phase shift introduced by the coupling capacitor.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with other advantages thereof, will be better understood by referring to the following description taken in connection with the accompanying drawing in which Fig. 1 illustrates a resistance-capacitance coupled amplifier embodying my invention; Fig. 2 is a schematic equivalent of the circuit shown in Fig. 1; Fig. 3 shows vectorially the phase shift of the coupling capacitor; and Fig. 4 shows vectorially how my invention neutralizes the phase shift of the coupling capacitor.

Referring to the drawing, I have illustrated in Fig. 1 a resistance-capacitance coupled amplifier having an input connected to the cathode and control element of an electron discharge device 1. The control element may be biased by a source of potential 2 connected between the cathode and the grid coupling resistor 3 which is connected to the control element. The anode of the electron discharge device is energized from a source of potential 4 through an anode coupling resistor 5. The anode is coupled to the control element of a second electron discharge device 6 by means of a coupling capacitor 7. The control element of the electron discharge device 6 is connected to a grid coupling resistor 8, and it may be biased bya source of potential 9 connected between the resistor 8 and the cathode. The anode of the electron discharge device 6 is supplied by current from a source of potential 10 through an anode coupling resistor 11. A coupling capacitor 12 is connected to the anode to provide an output circuit which is connected between the capacitor 12 and the cathode. provides a lead common to the cathodes of electron discharge devices 1 and 6, and the input and output circuits.

A capacitor 14 in'series with a resistor 15 is arranged in parallel with the anode coupling reslstor 5 to neutralize the phase shift introduced by the coupling capacitor. The resistor 15 and the capacitor 14 are so proportioned that the signal voltage component across the capacitor 14 is just sufficient to cause the signal voltage across the t anode coupling resistor 5 to lag the same amount that the signal voltage across grid coupling resistor 8 leads the signal voltage existing across the anode and cathode of the electron discharge device 1. capacitor 16 and a resistor 17 connected across the anode coupling resistor 11 to neutralize the phase shift introduced by the coupling capacitor l2.

In Fig. 2 of the drawing I have shown a schematic diagram of a circuit equivalent to that shown in Fig. 1. The electron discharge device 1 may be considered as a source of alternating potential E1 and the anode-to-cathode resistance of the device 1 is shown as R1. The anode circuit is represented by Hit in series with C14, and R5 in parallel therewith. The coupling capacitor C1 is connected to Re which represents the grid circuit resistance of the electron discharge device 6.

The effect of the phase shift introduced by the coupling capacitor C1 is shown in the vector diagram of Fig. 3. The voltage component across the resistor Rs is equal to E3 and the current Is, flowing in R6, is in phase with the voltage E3. This voltage E3 and current It may be shownvectorially as a horizontal line. The voltage E07 across the coupling capacitor C7 is in quadrature to the current 16 flowing through the capacitor. The vectorial resultant of the voltages E3 and E07 is the voltage E2 which lags the voltage E; by an angle 9. This represents the amount of phase shift which must be neutralized so that the voltage E3 will be' in phase with the voltage E1.

The vector diagram shown in Fig. 4 illustrates how the capacitor 14 and the resistor 15 neutralize the phase shift of the coupling capacitor '7. The voltage present across the resistor R15 is in phase with the current I15 flowing" through it and may be plotted as a horizontal A connection 13 The electron discharge device 6 has a line Ema in phase with the current vector In. The voltage E014 across the capacitor C14 is lagging the current 115 by 90 and thus is shown in quadrature to the voltage Ems. The vectorial sum of the voltage Ems and the voltage Eon is equal to the total voltage across the resistorRis and capacitor C14 which is the voltage E2. The current It flowing through the resistor R5 is in phase with the voltage E2. The current 11 flowing through the resistor R1 is equal to the vector sum of the current I15 and the current It fiowing through the parallel branches of the anode circuit. The voltage drop through the resistor R1 developed by the current Ii'is equivalent to the voltage Em which is in phase with the current I1. The voltage E1 impressed across the resistors R1, R15 and the capacitor C14 is equal to the vectorial sum of the voltages Em, Ems, and E014 existing across the various circuit parts. The sum of the voltages Ems and Em may be obtained as a vector shown as Ems-l-Em which is then vectorially added to the vector voltage E014 to obtain the vector E1. By proper proportions of the resistor R15 and the capacitor C14, the voltage E2 may be caused to lag the voltage E1 by an angle 6. As the voltage E1 is displaced by an angle 6 from the voltage E2 the same amount as the voltage E3 is displaced from the voltage E2 and thus the voltage E3 is in phase with voltage E1.

It is obvious that the voltage E2 may be displaced from the voltage E1 by any desired angle to neutralize the phase shift introduced by the coupling capacitor 7. My invention has the advantage of providing an amplifier for use over a range including audio and radio frequencies, with means for neutralizing the phase shift introduced by the coupling capacitor.

While I have shown and described my invention in connection with certain specific embodiments, it will, of course, be understood that I do not wish to be limited thereto, since it is apparent that the principles herein disclosed are susceptible of numerous other applications, and modifications may be made in the circuit arrangements and in the instrumentalities employed without departing from the spirit and scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a resistance-capacitance coupled amplifier for operation over a wide range of audible and super-audible frequencies, the combination of a resistor in series with a capacitor connected between the anode and cathode of an electron discharge amplifier of such magnitude that the phase shift introduced by the coupling capacitor is neutralized.

2. A resistance-capacitance coupled amplifier arranged to operate over a wide range of audio and radio frequencies including an electron discharge device having an anode, a cathode, and a control element, a coupling resistor connected between said anode and said cathode, a coupling capacitor connected to said anode for connection to the control element of a succeeding electron discharge device, a resistor in series with a menses capacitor and connected in parallel with said coupling resistor and having such magnitudes that the phase shift introduced by said coupling capacitor is neutralized.

3. A resistance-capacitance coupled amplifier operating over a wide range of audio and radio frequencies including a pair of electron discharge devices each having a cathode, an anode and a control element, a coupling resistor connected between the cathode and anode of the first discharge device, a coupling resistor connected between the cathode and control element of the second discharge device, a coupling capacitor connected between the anode of one electron discharge device and the control element of the other of said electron discharge devices, said ca pacitor normally introducing a phase shift, a resistor in series with a capacitor arranged between the anode and cathode of said first electron discharge device in parallel to said coupling resistor and having such magnitudes that the phase shift introduced by said coupling capacitor is neutralized.

4. A resistance-capacitance coupled amplifier for operation over a wide range of frequencies comprising audio and radio frequencies, said resistance-capacitance coupled amplifier including an electron discharge device having a cathode, an anode and a control element, an output circuit for said device including a coupling resistor connected to said anode and cathode, a capacitor connected to said anode for coupling said electron discharge device to the input circuit of a succeeding electron discharge device, and means connected in parallel with said anode coupling resistor and having a reactive component sufilcient for neutralizing the phase shift introduced by said capacitor.

5. In combination, an electron discharge device, a load device, a coupling capacitor connected between said eIectron discharge device and said load device whereby the voltage supplied to said load device is shifted in phase with respect to the output voltage of said electron discharge device, and means connected in shunt to said electron discharge device on the side adjacent to said coupling capacitor, said means producing a reactive component sufficient to neutralize 'said phase shift thereby to maintain the voltage on the load device in phase with the output voltage of said electron discharge device.

6. An audio and radio frequency amplifier comprising an electron discharge device having a cathode, an anode and a control element, a coupling resistor connected between said anode and said cathode, a load circuit for said device, a coupling capacitor connected between said anode and said load circuit, said coupling capacitor normally introducing a phase shift between the signal voltage generated by the device and the signal voltage supplied to said load circuit, and a resistor in series with a capacitor connected between said anode and said cathode and having such magnitudes so as to produce a reactive component suflicient to neutralize the phase shift introduced by said output coupling capacitor.

WILLIAM A. FITCH. 

